It is well known to multiplex digital signals, for example telephone voice channel signals (so-called DS-0 signals) at a bit rate of 64 kbps (kilobits per second), to produce higher bit rate signals for transmission, for example so-called DS-1, DS-2, and DS-3 signals. Various framing, stuffing, and control schemes are involved in the production of such multiplexed signals. As a result, neither the individual channels nor the multiplexed carriers are accessible in higher bit rate multiplexed signals. For example, DS-0 signals are not accessible in DS-2 and higher level multiplexed signals, and DS-1 signals are not accessible in DS-3 and higher level multiplexed signals. Such signals can only be accessed, for example to be switched, by demultiplexing the higher bit rate signals. This gives rise to extensive and costly multiplexing and demultiplexing equipment throughout present digital communications networks.
An object of this invention, therefore, is to provide an improved method of multiplexing digital signals.